Rechargeable positive electrode

ABSTRACT

Disclosed are battery cells comprising a sulfur-based positive composite electrode. Preferably, said cells are secondary cells, and more preferably thin film secondary cells. In one aspect, the cells can be in a solid-state or gel-state format wherein either a solid-state or gel-state electrolyte separator is used. In another aspect of the invention, the cells are in a liquid format wherein the negative electrode comprises carbon, carbon inserted with lithium or sodium, or a mixture of carbon with lithium or sodium. The novel battery systems of this invention have a preferred operating temperature range of from -40° C. to 145° C. with demonstrated energies and powers far in excess of state-of-the-art high-temperature battery systems.

This is a divisional of copending application Ser. No. 08/344,384 filedon Nov. 23, 1994.

FIELD OF USE

This invention relates generally to a positive electrode characterizedby active-sulfur. The electrodes are preferably rechargeable, and insome preferred embodiments are constructed in a thin-film format.Various negative electrodes, such as, alkali metal, alkaline earthmetal, transition metal, and carbon insertion electrodes, among others,can be coupled with the positive electrode to provide battery cells,preferably having high specific energy (Wh/kg) and energy density(Wh/l).

BACKGROUND OF THE INVENTION

The rapid proliferation of portable electronic devices in theinternational marketplace has led to a corresponding increase in thedemand for advanced secondary batteries. The miniaturization of suchdevices as, for example, cellular phones, laptop computers, etc., hasnaturally fueled the desire for rechargeable batteries having highspecific energies (light weight). Mounting concerns regarding theenvironmental impact of throwaway technologies, has caused a discernibleshift away from primary batteries and towards rechargeable systems.

In addition, heightened awareness concerning toxic waste has motivated,in part, efforts to replace toxic cadmium electrodes in nickel/cadmiumbatteries with the more benign hydrogen storage electrodes innickel/metal hydride cells. For the above reasons, there is a strongmarket potential for environmentally benign secondary batterytechnologies.

Secondary batteries are in widespread use in modem society, particularlyin applications where large amounts of energy are not required. However,it is desirable to use batteries in applications requiring considerablepower, and much effort has been expended in developing batteriessuitable for high specific energy, medium power applications, such as,for electric vehicles and load leveling. Of course, such batteries arealso suitable for use in lower power applications such as cameras orportable recording devices.

At this time, the most common secondary batteries are probably thelead-acid batteries used in automobiles. Those batteries have theadvantage of being capable of operating for many charge cycles withoutsignificant loss of performance. However, such batteries have a lowenergy to weight ratio. Similar limitations are found in most othersystems, such as Ni-Cd and nickel metal hydride systems.

Among the factors leading to the successful development of high specificto energy batteries, is the fundamental need for high cell voltage andlow equivalent weight electrode materials. Electrode materials must alsofulfill the basic electrochemical requirements of sufficient electronicand ionic conductivity, high reversibility of the oxidation/reductionreaction, as well as excellent thermal and chemical stability within thetemperature range for a particular application. Importantly, theelectrode materials must be reasonably inexpensive, widely available,non-toxic, and easy to process.

Thus, a smaller, lighter, cheaper, non-toxic battery is sought for thenext generation of batteries. The low equivalent weight of lithiumrenders it attractive as a battery electrode component for improvingweight ratios. Lithium provides also greater energy per volume than dothe traditional battery standards, nickel and cadmium..

The low equivalent weight and low cost of sulfur and its nontoxicityrenders it also an attractive candidate battery component. Successfullithium/organosulfur battery cells are known. [See, De Jonghe et al.,U.S. Pat. Nos. 4,833,048 and 4,917,974; and Visco et al., U.S. Pat. No.5,162,175.]

However, employing a positive electrode based on elemental sulfur in analkali metal-sulfur battery system has been considered problematic.Although theoretically the reduction of sulfur to an alkali metalsulfide confers a large specific energy, sulfur is known to be anexcellent insulator, and problems using it as an electrode have beennoted. Such problems referred to by those in the art include thenecessity of adjoining the sulfur to an inert electronic conductor, verylow percentages of utilization of the bulk material, poor reversibility,and the formation of an insulating sulfur film on the carbon particlesand current collector surface that electronically isolates the rest ofthe electrode components. [DeGott, P., "Polymere Carbone-Soufre Syntheseet Proprietes Electrochimiques," Doctoral Thesis at the InstitutNational Polytechnique de Grenoble (date of defense of thesis: 19 June1986) at page 117.]

Similarly, Rauh et al., "A Lithium/Dissolved Sulfur Battery with anOrganic Electrolyte," J. Electrochem. Soc., 126 (4): 523 (April 1979)state at page 523: "Both S₈ and its ultimate discharge product, Li₂ S,are electrical insulators. Thus it is likely that insulation of thepositive electrode material . . . led to the poor results for Li/Scells."

Further, Peramunage and Licht, "A Solid Sulfur Cathode for AqueousBatteries," Science, 261:1029 (20 August 1993) state at page 1030: "Atlow (room) temperatures, elemental sulfur is a highly insoluble,insulating solid and is not expected to be a useful positive electrodematerial." However, Peramunage and Licht found that interfacing sulfurwith an aqueous sulfur-saturated polysulfide solution converts it froman insulator to an ionic conductor.

The use of sulfur and/or polysulfide electrodes in non-aqueous oraqueous liquid-electrolyte lithium batteries (that is, in liquidformats) is known. For example, Peled and Yamin, U.S. Pat. No.4,410,609, describe the use of a polysulfide positive electrode Li₂S_(x) made by the direct reaction of Li and S in tetrahydrofuran (THF).Poor cycling efficiency typically occurs in such a cell because of theuse of a liquid electrolyte with lithium metal foil, and the Peled andYamin patent describes the system for primary batteries. Rauh et al.,"Rechargeable Lithium-Sulfur Battery (Extended Abstract), J. PowerSources, 26:269 (1989) also notes the poor cycling efficiency of suchcells and states at page 270 that "most cells failed as a result oflithium depletion."

Other references to lithium-sulfur battery systems in liquid formatsinclude the following: Yamin et al., "Lithium Sulfur Battery," J.Electrochem. Soc., 135(5): 1045 (May 1988); Yamin and Peled,"Electrochemistry of a Nonaqueous Lithium/Sulfur Cell," J. PowerSources, 9:281 (1983); Peled et al., "Lithium-Sulfur Battery: Evaluationof Dioxolane-Based Electrolytes," J. Electrochem. Soc., 136(6): 1621(June 1989); Bennett et al., U.S. Pat. No. 4,469,761; Farrington andRoth, U.S. Pat. No. 3,953,231; Nole and Moss, U.S. Pat. No. 3,532,543;Lauck, H., U.S. Pat. Nos. 3,915,743 and 3,907,591; Societe desAccumulateurs Fixes et de Traction, "Lithium-sulfur battery," Chem.Abstracts, 66: Abstract No. 111055d at page 10360 (1967); and Lauck, H."Electric storage battery with negative lithium electrode and positivesulfur electrode," Chem. Abstracts, 80: Abstract No. 9855 at pages466-467 (1974).]

DeGott, supra, notes at page 118 that alkali metal-sulfur batterysystems have been studied in different formats, and then presents theproblems with each of the studied formats. For example, he notes that an"all liquid" system had been rapidly abandoned for a number of reasonsincluding among others, problems of corrosiveness of liquid lithium andsulfur, of lithium dissolving into the electrolyte provokingself-discharge of the system, and that lithium sulfide forming in thepositive (electrode) reacts with the sulfur to give polysulfides Li₂S_(x) that are soluble in the electrolyte.

In regard to alkali metal-sulfur systems wherein the electrodes aremolten or dissolved, and the electrolyte is solid, which function inexemplary temperature ranges of 130° C. to 180° C. and 300° C. to 350°C., DeGott states at page 118 that such batteries have problems, suchas, progressive diminution of the cell's capacity, appearance ofelectronic conductivity in the electrolyte, and problems of safety andcorrosion. DeGott then lists problems encountered with alkalimetal-sulfur battery systems wherein the electrodes are solid and theelectrolyte is an organic liquid, and by extension wherein the negativeelectrode is solid, the electrolyte is solid, and the positive electrodeis liquid. Such problems include incomplete reduction of sulfur,mediocre reversibility, weak maximum specific power (performance limitedto slow discharge regimes), destruction of the passivating layer of Li₂S as a result of its reaction with dissolved sulfur leading to theformation of soluble polysulfides, and problems with the stability ofthe solvent in the presence of lithium.

DeGott also describes on page 117 a fundamental barrier to goodreversibility as follows. As alkali metal sulfides are ionic conductors,they permit, to the degree that a current collector is adjacent tosulfur, the propagation of a reduction reaction. By contrast, theirreoxidation leads to the formation of an insulating sulfur layer on thepositive electrode that ionically insulates the rest of the composite,resulting in poor reversibility.

DeGott concludes on page 119 that it is clear that whatever format isadopted for an alkali metal-sulfur battery system that the insulatingcharacter of sulfur is a major obstacle that is difficult to overcome.He then describes preliminary electrochemical experiments with acomposite electrode prepared by depositing on stainless steel bycapillary action a layer from a composition consisting in percent byweight: sulfur (46%); acetylene black (16%) and (PEO)₈ LiClO₄ (38%;polyethylene oxide/lithium perchlorate). From those preliminaryexperiments, DeGott concludes on page 128 that it is clear that, evenwhen optimizing the efficiency of the composite electrode (that is, bymultiplying the triple point contacts) that elemental sulfur cannot beconsidered to constitute an electrode for a secondary battery, in an"all solid" format.

Present solid-state lithium secondary battery systems are limited to aspecific energy of about 120 Wh/kg. It would be highly desirable to havea battery system characterized by higher specific energy values.

It would be even more desirable if solid-state batteries havingpractical specific energy values greater than about 150 Wh/kg couldoperate at room temperature. It would be additionally advantageous ifsolid-state batteries having high specific energy and operation at roomtemperature could be reliably fabricated into units with reproducibleperformance values.

In lithium cells wherein a liquid electrolyte is used, leakage of theelectrolyte can leave lithium exposed to the air, where it rapidlyreacts with water vapor and oxygen. Substantial casing can prevent suchreactions and protect users and the environment from exposure tohazardous, corrosive, flammable or toxic solvents but adds unwantedweight to the battery. A solid-state battery would greatly reduce suchproblems of electrolyte leakage and exposure of lithium, and would allowreducing the weight of the battery.

Furthermore, a battery formulation that overcomes the problem of lithiumdepletion described in the prior art, for example, Rauh et al., supra,would have many advantages.

In summary, disadvantages in currently available metal-sulfur batterysystems include poor cycling efficiency, poor reversibility, lithiumdepletion, or operating temperatures above 200° C., among otherproblems. Practitioners in the battery art have long sought asolid-state or gel-state metal-sulfur battery system that would overcomethese limitations.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a positive electrode for abattery cell that has low equivalent weight and high cell voltage andconsequently a high specific energy, and operates in a wide range oftemperatures including ambient and sub-ambient temperatures. Anexemplary operating temperature range for the batteries of thisinvention is from -40° C. to 145° C. The batteries of this invention arepreferably rechargeable. Thin film type battery cells are preferredembodiments.

The positive electrode of this invention comprise an active-sulfur-basedmaterial having a relatively low equivalent weight. Said electrode is acomposite comprising, in the theoretically fully charged state,elemental sulfur, preferably an ionically conductive material, and anelectronically conductive material. Upon discharge, the active sulfur ofthe positive electrode reacts with the metal of the negative electrode,and metal sulfides and polysulfides form. For example, where M is themetal of the negative electrode, the overall cell reaction can bedescribed as follows:

    x/zM+S=M.sub.x/z S

wherein M=any metal that can function as an active component in anegative electrode in a battery cell wherein active-sulfur is the activecomponent of the positive electrode; x=0 through x=2; z=the valence ofthe metal; and S is sulfur.

M is preferably selected from the group consisting of alkali metals,alkaline earth metals, and transition metals. M is more preferablyselected from the group consisting of alkali metals, and still morepreferably lithium or sodium. M is most preferably lithium.

More specifically, for example, in a preferred embodiment of thisinvention wherein the negative electrode contains lithium, the overallcell reaction wherein z=1 can be described as follows:

    xLi+S=Li.sub.x S.

When x=2, 100% of the theoretical specific energy of the system has beenreleased.

Upon discharge, the positive electrode becomes a combination of sulfur,metal sulfides and polysulfides, and during the discharging process theproportions of those sulfur-containing components will change accordingto the state of charge. The charge/discharge process in the positiveelectrode is reversible. Similarly, upon recharging, the percentages ofthe sulfur-containing ingredient will vary during the process.

The positive electrode is thus made from an electrode compositioncomprising active-sulfur, an electronically conductive materialintermixed with the active-sulfur in a manor that permits electrons tomove between the active-sulfur and the electronically conductivematerial, and an ionically conductive material intermixed with theactive-sulfur in the manor that permits ions to move between theionically conductive material and the sulfur.

The ionically conductive material of said composite positive electrodeis preferably a polymeric electrolyte, more preferably a polyalkyleneoxide, and further, preferably polyethylene oxide in which anappropriate salt may be added. Additional ionically conductive materialsfor use in the positive electrode include the components decribed in thesolid-state and gel-state electrolyte separator.

Examples of electronically conductive materials of the compositepositive electrode include carbon black, electronically conductivecompounds with conjugated carbon-carbon and/or carbon-nitrogen doublebonds, for example but not limited to, electronically conductivepolymers, such as, polyaniline, polythiophene, polyacetylene,polypyrrole, and combinations of such electronically conductivematerials. The electronically conductive materials of the positiveelectrode may also have electrocatalytic activity.

The composite sulfur-based positive electrode may further optionallycomprise performance enhancing additives, such as, binders;electrocatalysts, for example, phthalocyanines, metallocenes, brilliantyellow [Reg. No. 3051-11-4 from Aldrich Catalog Handbook of FineChemicals; Aldrich Chemical Company, Inc., 1001 West Saint Paul Avenue,Milwaukee, Wis. 53233 (USA)] among other electrocatalysts; surfactants;dispersants (for example, to improve the homogeneity of the electrode'singredients); and protective layer forming additives (for example, toprotect a lithium negative electrode), such as, organosulfur compounds,phosphates, iodides, nitrides, and fluorides, for example LiI and HF.

The range of active-sulfur in such electrodes in the theoretically fullycharged state is from 20% to 80% by weight. Said active-sulfur-basedcomposite electrode is preferably processed such that the componentparticles are homogeneously distributed, and segregation and/oragglomeration of the component particles is avoided.

A metal-sulfur battery systems constructed with said active-sulfur-basedcomposite positive electrode of this invention should have at least 5%,and more preferably at least 10% availability of the active-sulfur. Thatavailability corresponds to a minimum of 168 mAh per gram of sulfurincluded in the positive electrode. This is based the theoretical valueof 1675 mAh/gm of sulfur at 100% availability. Thus, between about 10%and about 100% of the active-sulfur is accessible to any chargecarriers.

The electrolyte separator used in combination with the positiveelectrodes of this invention functions as a separator for the electrodesand as a transport medium for the metal ions. Any electronicallyinsulating and ionically conductive material which is electrochemicallystable may be used. For example, it has been shown that polymeric, glassand/or ceramic materials are appropriate as electrolyte separators, aswell as other materials known to those of skill in the art, such as,porous membranes and composites of such materials. Preferably, however,the solid-state electrolyte separator is any suitable ceramic, glass, orpolymer electrolyte such as, polyethers, polyimines, polythioethers,polyphosphazenes, polymer blends, and the like, in which an appropriateelectrolyte salt may be added. In the solid-state, the electrolyteseparator may contain an aprotic organic liquid wherein said liquidconstitutes less than 20% (weight percentage) of the total weight of theelectrolyte separator.

In the gel-state, the electrolyte separator contains at least 20%(weight percentage) of an aprotic organic liquid wherein the liquid isimmobilized by the inclusion of a gelling agent. Any gelling agent, forexample, polyacrylonitrile, PVDF, or PEO, can be used.

The liquid electrolyte for the liquid format batteries using thepositive electrode of this invention, is also preferably an aproticorganic liquid. The liquid format battery cells constructed using thepositive electrodes of this invention would preferably further comprisea separator which acts as an inert physical barrier within the liquidelectrolyte. Exemplary of such separators include glass, plastic,ceramic, polymeric materials, and porous membranes thereof among otherseparators known to those in the art.

Solid-state and gel-state positive electrodes of this invention can beused in solid-state or liquid format batteries, depending on thespecific format of the electrolyte separator and negative electrode.Regardless of the format of the batteries using the positive electrodeof this invention, the negative electrode can comprise any metal, anymixture of metals, carbon or metal/carbon material capable offunctioning as a negative electrode in combination with theactive-sulfur-based composite positive electrode of this invention.Accordingly, negative electrodes comprising any of the alkali oralkaline earth metals or transition metals for example, (the polyetherelectrolytes are known to transport divalent ions such as Zn⁺⁺) incombination with the positive electrode of this invention are within theambit of the invention, and particularly alloys containing lithiumand/or sodium.

Preferred materials for said negative electrodes include Na, Li andmixtures of Na or Li with one or more additional alkali metals and/oralkaline earth metals. The surface of such negative electrodes can bemodified to include a protective layer, such as that produced on thenegative electrode by the action of additives, including organosulfurcompounds, phosphates, iodides, nitrides, and fluorides, and/or an inertphysical barrier conductive to the metal ions from the negativeelectrode, for example, lithium ions transport in lithium phosphate, orsilicate glasses, or a combination of both.

Also preferred materials for said negative electrodes include carbon,carbon inserted with lithium or sodium, and mixtures of carbon withlithium or sodium Here, the negative electrode is preferrably carbon,carbon inserted with lithium or sodium, and/or a mixture of carbon withlithium or sodium. When the negative electrode is carbon, the positiveelectrode is in the fully discharged state, comprising lithium or sodiumsulfides and polysulfides. Particularly preferred negative electrodesfor batteries are lithium inserted within highly disordered carbons,such as, poly p-phenylene based carbon, graphite intercalationcompounds, and Li_(y) C₆ wherein y=0.3 to 2, for example, LiC₆, Li₂ C₆and LiC₁₂. When the negative electrode is carbon, the cells arepreferably assembled with the positive electrode in the fully dischargedstate comprising lithium or sodium sulfides and/or polysulfides. The useof negative electrodes of the carbon, carbon inserted with lithium orsodium, and mixtures of carbon with lithium or sodium with thesolid-state and gel-state positive electrodes of this invention areespecially advantageous when the battery is in the liquid fount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic of a Li/electrolyte separator/active-sulfurelectrode cell of this invention.

FIG. 2 illustrates the reversible cycling performance of a lithium cell(Li/amorphous PEO/active-sulfur) of this invention evaluated at 30° C.at an active-sulfur capacity of 330 mAh/gm for each cycle.

FIG. 3 illustrates the availability of the active-sulfur in the positiveelectrode of a lithium cell (Li/amorphous PEO/active-sulfur) of thisinvention evaluated at 30° C.

FIG. 4 illustrates the availability of the active-sulfur in the positiveelectrode of a lithium cell (Li/gel-state electrolyteseparator/active-sulfur) of this invention evaluated at 30° C.

FIG. 5 illustrates the availability of the active-sulfur in the positiveelectrode of a lithium cell (Li/PEO/active-sulfur) of this inventionevaluated at 90° C.

FIG. 6 illustrates the reversible cycling performance of a lithiumcell-(Li/PEO/active-sulfur) of this invention evaluated at 90° C. at anactive-sulfur capacity of 400 mAh/gm for each cycle.

FIG. 7 illustrates the reversible cycling performance of a lithium cell(Li/PEO/active-sulfur) of this invention evaluated at 90° C.

FIG. 8 illustrates the peak power performance of a lithium cell(Li/PEO/active-sulfur) of this invention evaluated at 90° C.

Abbreviations

aPEO--amorphous polyethylene oxide

cm--centimeter

DEC--diethyl carbonate

DMC--dimethyl carbonate

DME--dimethyl ether

EC--ethylene carbonate

E.W.--equivalent weight

F.W.--formula weight

GICs--graphite intercalation compounds

gm--gram

mAh--milliamperes per hour

mm--millimeter

MW--molecular weight

OCV--open circuit voltage

PC--propylene carbonate

P.E.D.--practical energy density

PEO--polyethylene oxide

PEG--polyethylene glycol

PPP--poly (p-phenylene)

psi--pounds per square inch

PVDF--polyvinylidene fluoride

T.E.D.--theoretical energy density

μA--microampere

μm--micrometer

WE--working electrode

W/kg--watts per kilogram

Wh/kg--watthours per kilogram

W/I--watts per liter

wt.--weight

V--volts

Definitions

"Metals" are defined herein to be elements whose atoms usually loseelectrons in the formation of compounds.

The phrase "alkali metals" is herein defined as the alkali family ofmetals located in Group IA of the periodic table, including lithium(Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) andfrancium (Fr).

The phrase "alkaline earth family" is herein defined as the Group IIAelements, including beryllium (Be), magnesium (Mg), calcium (Ca),strontium (St), barium (Ba) and radium (Ra).

The phrase "transition metals" is defined herein to include thefollowing metals:

(1) the scandium family: scandium (Sc), yttrium (Y), lanthanum (La) andthe lanthanide series, and actinium (Ac) and the actinide series;

(2) the titanium family: titanium (Ti), zirconium (Zr), and hafnium(Hf);

(3) the vanadium family: vanadium (V), niobium (Nb), and tantalum (Ta);

(4) the chromium family: chromium (Cr), molybdenum (Mo), and tungsten(W);

(5) the manganese family: manganese (Mn), technetium (Tc), and rhenium(Re);

(6) the iron family: iron (Fe), cobalt (Co), and nickel (Ni);

(7) the platinum family: ruthenium (Ru), rhodium (Rh), palladium (Pd),osmium (Os), iridium (Ir), and platinum (Pt);

(8) the copper family: copper (Cu), silver (Ag), and gold (Au);

(9) the zinc family: zinc (Zn), cadmium (Cd), and mercury (Hg);

(10) the aluminum family: aluminum (Al), gallium (Ga), indium (In), andthallium (Tl); and

(11) the germanium family: germanium (Ge), tin (Sn), and lead (Pb).

The term "active-sulfur" is defined herein to be elemental sulfur orsulfur that would be elemental if the positive electrode were in itstheoretically fully charged state.

The term "solid-state" is defined herein to be a material which containsless than 20% by weight of a liquid.

The term "gel-state" is defined herein to be a material containing atleast 20% by weight of a liquid wherein said liquid is immobilized bythe presence of a gelling agent.

The term "component" is defined herein to be (a) positive electrode, (b)electrolyte separator, or (c) negative electrode.

DETAILED DESCRIPTION

The instant invention provides a positive electrode for solid-state andliquid format battery systems, wherein the positive electrode is basedon active-sulfur, which provides high specific energy and power,exceeding that of highly developed systems now known and in use.Solid-state format battery cell means all the components of the batteryare either solid-state or gel-state. It further means that no componentis in a liquid state. The equivalent weight of the active-sulfur used inthe redox reactions within the battery cells of this invention is 16grams/equivalent (with a lithium metal as the negative electrode,active-sulfur in its theoretically fully discharged state is Li₂ S),leading to a theoretical specific energy of 2800 watthours per kilogram[Wh/kg] for a lithium cell having a average OCV of 2.4 volts. Such anexceedingly high specific energy is very unusual and highly attractive.

Further, the batteries containing the positive electrode of thisinvention can operate at room temperature. The battery systems of thisinvention provide energy to weight ratios far in excess of the presentdemands for load leveling and/or electric vehicle applications, and canbe reliably fabricated into units with reproducible performance values.

This invention can be incorporated in a battery cell which includessolid-state or gel-electrolyte separators. This embodiment excludes theproblem of a battery cell in the liquid format that may sufferelectrolyte leakage. For example, in lithium cells wherein a liquidelectrolyte is used, leakage of the electrolyte can leave lithiumexposed to the air, where it rapidly reacts with water vapor.Substantive casing can prevent such reactions and protects users and theenvironment from exposure to solvents but adds unwanted weight to thebattery. Using a solid-state or gel-state format battery cells greatlyreduces such problems of electrolyte leakage and exposure of lithium,and can cut down on the weight of the battery.

Another embodiment concerns battery cells in a liquid format, which havea solid active-sulfur-based positive electrode of this invention, andwhich have a solid negative electrode that contains carbon (when in thefully discharged state), carbon inserted with lithium or sodium and/or amixture of carbon with lithium or sodium. Such an embodiment canovercome the problem of lithium depletion described in the prior art,for example, Rauh et al., supra.

In accordance with this invention, the active-sulfur-based compositepositive electrode and a battery system constructed with said positiveelectrode are provided. The positive electrodes of this invention arepreferably reversible, and the metal-active-sulfur battery cells arepreferably secondary batteries, and more preferably thin film secondarybatteries.

The invention relates in one aspect to the positive electrode of batterycells wherein both the positive and negative electrodes are solid-stateor gel-state and the electrolyte separator is either a solid-state or agel-state material (see Definition). In another aspect, as indicatedabove, the positive electrode of this invention is used in a batterycell which contains a liquid electrolyte wherein the negative electrodeis solid or gel-state and contains carbon, carbon inserted with lithiumor sodium, or mixtures of carbon with lithium or sodium. However,whatever the format of the battery cells made with the positiveelectrodes of this invention, said positive electrode compriseselemental sulfur as the active component when in the theoretically fullycharged state.

Positive Electrode

The active-sulfur of the novel positive electrodes of this invention ispreferably uniformly dispersed in a composite matrix, for example, theactive-sulfur can be mixed with a polymer electrolyte (ionicallyconductive), preferably a polyalkylene oxide, such as polyethylene oxide(PEO) in which an appropriate salt may be added, and an electronicallyconductive material. Furthermore, the ionically conductive material maybe either solid-state or gel-state format. In most cases it will benecessary or desirable to include a suitable polymeric electrolyte, forrapid ion transport within the electrode as is done with intercalationmaterials based electrodes. In a preferred embodiment, the ionicallyconducting material is polyethylene oxide or amorphous polyethyleneoxide complexed with lithium trifluoromethanesulfonimide and having aconcentration of between about 1:8 and about 1:49 molecules of salt permonomer unit. Furthermore, because the active-sulfur is not electricallyconductive, it is important to disperse some amount of an electronicallyconductive material in the composite electrode.

Preferred weight percentages of the major components of theactive-sulfur-based positive electrodes of this invention in atheoretically fully charged state are: from 20% to 80% active-sulfur;from 15% to 75% of the ionically conductive material (which may begel-state or solid-state), such as PEO with salt, and from 5% to 40% ofan electronically conductive material, such as carbon black,electronically conductive polymer, such as polyaniline. More preferably,those percentages are: from 30% to 75% of active-sulfur; from 15% to 60%of the ionically conductive material; and from 10% to 30% of theelectronically conductive material. Even more preferable percentagesare: from 40% to 60% of active-sulfur; from 25% to 45% of the ionicallyconductive material; and from 15% to 25% of the electronicallyconductive material. Another preferred percentage by weight range forthe electronically conductive material is from 16% to 24%.

Methods of Making a Positive Electrode:

The positive electrode of this invention can be prepared for each of thebattery formats by a combination of generally known processes. Forexample, for a solid-state format, the active-sulfur material,polyethylene oxide (PEO) and carbon black can be dissolved or dispersedin acetonitrile using PEG dispersant, and subsequently the solvent canbe evaporated to east a thin film (for example, from 10 to 200 microns)of a solid composite electrode on a surface. In a preferred embodiment,the positive electrode is composed of active-sulfur, PEO (conventionalor amorphous) and carbon black.

The ionic conductors in the positive electrode of this invention can beany of the solid-state or gel-state electrolytes described in theElectrolyte Separators and Liquid Electrolytes section but are notlimited to those described in that section.

The composite electrode of this invention is preferably prepared suchthat homogeneity of the product is obtained. Segregation of thecomponents is preferably avoided. For example, in processing thepositive electrodes of this invention, it is generally advisable toprevent segregation of the active-sulfur to the current collectorelectrode interface. The processing should render the sulfur generallyavailable and at least 10% available. Also avoided is agglomeration ofany component particles or grains. Thus, relatively uniform distributionof the components is preferably sought.

The metal-sulfur battery systems constructed with said active-sulfurbased composite positive electrode of this invention should have atleast 5%, and more preferably at least 10% at availability of theactive-sulfur. That availability corresponds to a minimum of 84 mAh pergram of active-sulfur included in the positive electrode. This is basedthe theoretical value of 1675 mAh/gm of sulfur as 100% availability.

Positive electrode films can be made by mixing 45%-55% (percentage byweight) elemental sulfur, 8-24% carbon black, and the balance includesbut is not limited to ionic conductors such as amorphous polyethyleneoxide (aPEO: oxymethylene-linked polyethylene oxide) or polyethyleneoxide (PEO) based electrolytes. The ionic conductors can also containadded anhydrous electrolyte salts such as lithiumtrifluoromethanesulfonimide or lithium perchlorate. All the componentsare added to a solvent such as acetonitrile. The solvent to ionicconductor ratio can is typically from 40-200 ml per gram of the ionicconductor.

The components are stir-mixed for approximately two days until theslurry appears well mixed and uniform. This positive electrode slurry iscast directly and immediately onto stainless steel current collectors,and the solvent is allowed to evaporate at ambient temperatures.Alternatively, the electrode film can be cast on a release film surfaceand then transferred from such surface to an electrical connector on acurrent collector. Conventional electrical connectors such as carbon oraluminum powders or fibers or mesh may be used. A typical resultingpositive electrode film weight ranged from approximately 0.0016 gm percm² through 0.0120 gm per cm².

Uniformity of mixing can be achieved by methods known to those skilledin the art, for example, by prolonged slurry mixing, shear mixing, ballmilling or vibromilling of the slurry, and cryogenic milling of thefrozen slurry. The homogeneous slurries thus obtained should bepreferably used immediately in subsequent electrode forming processes tominimize segregation or agglomeration of any of the components. Thesolvent, water, or liquid traces may be removed from the positiveelectrode slurry by exposing an electrode slurry film to a vacuum eitherwith or without the application of the heat. The components of theresulting electrode will be uniformly distributed such that eachcomponent's concentration does not differ by more than 25% in a samplevolume defined by the thin film thickness cubed.

Electrolyte Separators and Liquid Electrolytes

The electrolyte separator for solid-state format battery cellsincorporating the positive electrode of this invention functions as aseparator for the positive and negative electrodes and as a transportmedium for the metal ions. As defined above, the material for such anelectrolyte separator is preferably electronically insulating, ionicallyconductive and electrochemically stable.

When the battery cell is in a solid-state format, all components areeither solid-state or gel-state and no component is in the liquid state.

The aprotic organic liquids used in the electrolyte separators of thisinvention, as well as in the liquid electrolytes of this invention, arepreferably of relatively low molecular weight, for example, less than50,000 MW. Combinations of aprotic organic liquids may be used for theelectrolyte separators and liquid electrolytes of the battery cellsincorporating the positive electrode of this invention.

Preferred aprotic organic liquids of the battery cells incorporating thepositive electrode of this invention include among other related aproticorganic liquids, sulfolane, dimethyl sulfone, dialkyl carbonates,tetrahydrofuran (THF), dioxolane, propylene carbonate (PC), ethylenecarbonate (EC), dimethyl carbonate (DMC), butyrolactone,N-methylpyrrolidinone, tetramethylurea, glymes, ethers, crown ethers,dimethoxyethane (DME), and combinations of such liquids.

For the battery cells, incorporating the positive electrode of thisinvention, containing a liquid electrolyte wherein the negativeelectrode is carbon-containing, said liquid is also an aprotic organicliquid as described above. Such a format also preferably contains aseparator within the liquid electrolyte as discussed above.

An exemplary solid-state electrolyte separator combined with thisinvention is a ceramic or glass electrolyte separator which containsessentially no liquid. Polymeric electrolytes, porous membranes, orcombinations thereof are exemplary of the type of electrolyte separatorto which an aprotic organic plasticizer liquid could be added accordingto this invention for the formation of a solid-state electrolyteseparator containing less than 20% liquid.

Preferably the solid-state electrolyte separator is a solid ceramic orglass electrolyte and/or solid polymer electrolyte. Said solid-stateceramic electrolyte separator preferably comprises a beta alumina-typematerial, Nasicon or Lisicon glass or ceramic. The solid-stateelectrolyte separator may include sodium beta alumina or any suitablepolymeric electrolyte, such as polyethers, polyimines, polythioethers,polyphosphazenes, polymer blends, and the like and mixtures andcopolymers thereof in which an appropriate electrolyte salt hasoptionally been added. Preferred polyethers are polyalkylene oxides,more preferably, polyethylene oxide.

Exemplary but optional electrolyte salts for the battery cellsincorporating the positive electrode of this invention include, forexample, lithium trifluoromethanesulfonimide [LiN(CF₃ SO₂)₂ ], lithiumtriflate (LiCF₃ SO₃), lithium perchlorate (LiClO₄), LiPF₆, LiBF₄,LiAsF₆, as well as, corresponding salts depending on the choice of metalfor the negative electrode, for example, the corresponding sodium salts.As indicated above, the electrolyte salt is optional for the batterycells of this invention, in that upon discharge of the battery, themetal sulfides or polysulfides formed can act as electrolyte salts, forexample, M_(x/z) S wherein x=0 to 2 and z is the valence of the metal.

Negative electrode

For solid-state battery cells incorporating the positive electrode ofthis invention, the negative electrode may comprise any metal, anymixture of metals, any carbon or metal/carbon material capable offunctioning as an active component of a negative electrode incombination with said sulfur positive electrode. For example, any of thealkali or alkaline earth metals or transition metals can be used, andparticularly mixtures containing lithium and/or sodium.

Preferred materials for said negative electrode for the solid-statebattery cell formats include sodium and/or lithium, and mixtures ofsodium or lithium with one or more additional alkali metals and/oralkaline earth metals. Preferred materials for said negative electrodealso include mixtures of sodium or lithium with one or more elements toform a binary or ternary alloy, such as, Na₄ Pb, lithium-silicon andlithium-aluminum alloys.

A particularly preferred metal for a negative electrode is sodium, or atleast a sodium base ahoy (i.e., at least 90% by weight sodium) becauseof its low cost, low equivalent weight and its relatively low meltingpoint of 97.8° C. However, other alkali metals such as Li or K, ormixtures of same with Na may also be used, as desired, to optimize theoverall system.

Also preferred negative electrode materials for the solid-state batterycells incorporating the positive electrode of this invention includecarbon, carbon inserted with lithium or sodium and/or a mixture ofcarbon with sodium or lithium. Exemplary and preferred are Li_(y) C₆(wherein y=0.3 to 2), such as, LiC₆, negative electrodes which comprisegraphite or petroleum coke, for example, graphite intercalationcompounds (GICs), and carbon inserted within highly disordered carbons.The inserted carbon may also be that wherein some carbon has beenalloyed with boron, or wherein the carbon has been prepared from lowtemperature pyrolysis (about 750° C.) of carbon or carbon-siliconcontaining polymers such that the carbon product retains some hydrogenor silicon or both. [See, Sato et al., "A Mechanism of Lithium Storagein Disordered Carbons," Science, 264:556 (22 April 1994), whichdiscusses very good results with a preferred negative electrode of Liinserted within poly p-phenylene-based (PPP-based) carbon.]

For battery cells using the positive electrode of this invention thatare in liquid formats, the negative electrode is carbon, carbon insertedwith lithium or sodium, or mixtures of carbon and lithium or sodium asdescribed above in relation to solid-state formats, including thepreferable versions of such carbon-containing electrodes. For whateverformat, if the negative electrode contains only carbon, the cell is inthe theoretically fully discharged state, and the positive electrodecomprises lithium or sodium sulfides or polysulfides.

Battery Cells

The battery cells containing the sulfur-based composite positiveelectrodes of this invention can be constructed according toconventional formats as described in the literature. For example, DeJonghe et al., U.S. Pat. No. 4,833,048 and Visco et al., U.S. Pat. No.5,162,175. Such conventional formats are understood to be hereinincorporated by reference.

The novel battery cells incorporating this invention, preferablysecondary cells, more preferably thin film secondary cells, my beconstructed by any of the well-known and conventional methods in theart. The negative electrode may be spaced from the positive sulfurelectrode, and both electrodes may be in material contact with anionically conductive electrolyte separator. Current collectors contactboth the positive and negative electrodes in a conventional manner andpermit an electrical current to be drawn by an external circuit.

Suitable battery constructions may be made according to the known artfor assembling cell components and cells as desired, and any of theknown configurations may be fabricated utilizing the invention. Theexact structures will depend primarily upon the intended use of thebattery unit.

A general scheme for the novel battery cells of this invention in asolid-state format may include a current collector in contact with thenegative electrode and a current collector in contact with the positiveelectrode, and a solid-state electrolyte separator sandwiched betweenthe negative and positive electrodes. In a typical cell, all of thecomponents will be enclosed in an appropriate casing, for example,plastic, with only the current collectors extending beyond the casing.Thereby, reactive elements, such as sodium or lithium in the negativeelectrode, as well as other cell elements are protected.

The current collectors can be sheets of conductive material, such as,aluminum or stainless steel, which remain substantially unchanged duringdischarge and charge of the cell, and which provide current connectionsto the positive and negative electrodes of the cell. The positiveelectrode film may be attached to the current collector by directlycasting onto the current collector or by pressing the electrode filmonto the current collector. Positive electrode mixtures cast directlyonto current collectors preferably have good adhesion. Positiveelectrode films can also be cast or pressed onto expanded metal sheets.Alternately, metal leads can be attached to the positive electrode filmby crimp-sealing, metal spraying, sputtering or other techiques known tothose skilled in the art. The sulfur-based positive electrode can bepressed together with the electrolyte separator sandwiched between theelectrodes. In order to provide good electrical conductivity between thepositive electrode and a metal container, an electronically conductivematrix of, for example, carbon or aluminum powders or fibers or metalmesh may be used. Further,as is conventional in the art, such materialscan be used as electrical connectors between the positive electrode filmand the current collector.

A particularly preferred battery cell comprises a solid lithium orsodium electrode, a polymeric electrolyte separator, either solid-stateor gel, preferably a polyalkylene oxide, such as, polyethylene oxide,and a thin-film composite positive electrode containing an elementalsulfur electrode (that is hi the theoretically fully charged state), andcarbon black, dispersed in a polymeric electrolyte. Optionally theelectrolyte separator in such a preferred battery call can comprise anelectrolyte salt.

Operating Temperatures

The operating temperature of the battery cells incorporating the novelpositive electrode of this invention is preferably 180° C. or below.Preferred operating temperature ranges depend upon the application.Exemplary preferred operating temperature ranges include from -40° C. to145° C.; from -20° C. to 145° C.; from -20° C. to 120° C.; and from 0°C. to 90° C. Most preferably for many applications, the cellsincorporating this invention operate at ambient or above-ambienttemperatures.

Different embodiments of this invention can provide different preferredoperating temperature ranges. The choice of electrolyte can influencethe preferred operating temperature ranges for the batteriesincorporating the positive electrode of this invention. For example,when conventional PEO is used the preferred operating range is 60° C.;whereas when amorphous PEO (aPEO) is used, the battery can be run atroom temperature, or in a range of 0° C. to 60° C.

Gel formats also provide for lower operating temperature ranges.Exemplary battery cells using the positive electrode of this inventioncontaining, for example, polymeric electrolyte separators withincreasingly greater percentage of a aprotic organic liquid immobilizedby the presence of a gelling agent, can provide for increasingly loweroperating temperature ranges. An exemplary operating temperature rangefor a solid-state battery having gel-state components of this inventionwould be from about -20° C. to about 60° C.

A battery with a liquid separator and an negative electrode comprisingcarbon, inserted carbon and/or a mixture of carbon and lithium or sodiumcan operate at a preferred temperature range of from -40° C. to 60° C.

The high temperature operating range of the battery cells based on thepositive electrode of this invention can be limited by the melting pointof either a solid electrode or a solid electrolyte. Thus sodium negativeelectrodes are limited to temperatures below 97.8° C., but sodium ahoyelectrodes, such as Na₄ Pb, can be used in a solid form at well over100° C.

Specific Energy

The practical specific energies of the secondary cells utilizing thisinvention are preferably greater than 65 watt-hours per kilogram(Wh/kg), more preferably greater than 100 Wh/kg, still more preferablygreater than 150 Wh/kg, even more preferably greater than 200 Wh/kg,still even more preferably greater than 250 Wk/kg and even morepreferably greater than 850 Wh/kg. A preferred practical specific energyrange of the batteries incorporating this invention is from about 100Wh/kg to about 800 Wh/kg.

Cells made with lithium negative electrodes, solid-state or gel-stateelectrolyte separators, and positive electrodes made with sulfur,polyethylene oxide (or modified polyethylene oxide) and carbon particleswere constructed to test the performance of the batteries of thisinvention. Examples of these tests will serve to further illustrate theinvention but are not meant to limit the scope of the invention in anyway.

EXAMPLE 1 Solid-state cell: Cycling performance at an active-sulfurcapacity of 330 mAh/gm for each recharge cycle evaluated at 30° C.

A positive electrode film was made by mixing 45% (percentage by weight)elemental sulfur, 16% carbon black, amorphous polyethylene oxide (aPEO)and lithium trifluoromethanesulfonimide [wherein the concentration ofPEO monomer units (CH₂ CH₂ O) per molecule of salt was 49:1], and 5%2,5-dimercapto-1,3,4-dithiadiazole in a solution of acetonitrile (thesolvent to PEO ratio being 60:1 by weight). The components werestir-mixed for approximately two days until the slurry was well mixedand uniform. A thin positive electrode film was cast directly ontostainless steel current collectors, and the solvent was allowed toevaporate at ambient temperatures. The resulting positive electrode filmweighed approximately 0.0028 gm per cm².

The polymeric electrolyte separator was made by mixing aPEO with lithiumtrifluoromethanesulfonimide, [the concentration of the electrolyte saltto PEO monomer units (CH₂ CH₂ O) per molecule of salt being 39:1] in asolution of acetonitrile (the solvent to polyethylene oxide ratio being15:1 by weight). The components were stir-mixed for two hours until thesolution was uniform. Measured amounts of the separator slurry were castinto a retainer onto a release film, and the solvent was allowed toevaporate at ambient temperatures. The resulting electrolyte separatorfilm weighed approximately 0.0144 gm per cm².

The positive electrode film and polymeric electrolyte separator wereassembled under ambient conditions, and then vacuum dried overnight toremove moisture prior to being transferred into the argon glovebox forfinal cell assembly with a 3 rail (75 micron) thick lithium anode film[FMC/Lithco, 449 North Cox Road, Box 3925 Gastonia, N.C. 28054 (USA)].

A schematic of the cell layers are shown in FIG. 1. Once assembled, thecell was compressed at 2 psi and heated at 40° C. for approximately 6hours. After heating the layers of lithium, electrolyte separator, andthe positive electrode were well adhered.

The cell was then evaluated with a battery tester [Maccor Inc., 2805West 40th Street, Tulsa, Okla. 74107 (USA)] inside the glovebox at 30°C. That procedure was performed to eliminate any contamination problemsof the lithium.

The cell was cycled to a constant capacity corresponding to delivering330 mAh per gram of the active-sulfur in the positive electrode film.The rates used were 100-20 μA/cm² for discharging and 50-10 μA/cm² forcharging to cutoff voltages of 1.8 and 3.0 volts, respectively.

FIG. 2 shows the end of the discharge voltage of the cell after eachrecharge cycle. As evident from the graph, the cell performance is veryconsistent.

EXAMPLE 2 Solid-state cell: Total discharge capacity to 900 mAh/gm ofactive-sulfur evaluated at 30° C.

A cell identical to the one described in Example 1 was discharged to 1.8volts at current densities of 100-20 μA/cm² at 30° C. to determine thetotal availability of the active-sulfur in the film. The resultingdischarge curve is seen in FIG. 3. The total capacity delivered by thisfilm was in excess of 900 mAh per gram of the active-sulfur, that is, autilization of 54% of the available active-sulfur, wherein 100% would be1675 mAh/gm.

EXAMPLE 3 Solid-state cell having gel-state components: Total dischargecapacity to 900 mAh/gm of active-sulfur evaluated at 30° C.

A positive electrode film similar to the one described in Example 1 wasmade with a composition of 50% (percentage by weight) elemental sulfur,16% carbon black, amorphous polyethylene oxide (aPEO) and lithiumtrifluoromethanesulfonimide (at a 49:1 concentration).

The electrolyte separator used was a gel made inside the glovebox toavoid moisture and oxygen contamination. A starting solution consistingof 10% (weight percentage) of lithium trifluoromethanesulfonimide and90% of tetraethylene glycol dimethylether (tetraglyme) was made. Then asolvent of 90% tetrahydrofuran (THF) was mixed with 10% of the startingsolution. 5.6% Kynar Flex 2801 [Elf Atochem of North America, Inc.,Fluoropolymers Department, 2000 Market Street, Philadelphia, Pa. 19103(USA)], (hexafluoropropylene-vinylidene fluoride copolymer), a gellingagent, was added to the mixture.

The mixture was stirred for a few minutes and then left standing for 24hours so that the components were absorbed into thehexafluoropropylene-vinylidene fluoride copolymer. The mixture wasstirred again for a few minutes to homogenize the components and thenheated for 1 hour at 60° C. Electrolyte separator films were cast onto arelease film, and the THF solvent was allowed to evaporate at ambienttemperatures. The resulting electrolyte separator film weighedapproximately 0.0160 gm per cm².

The resulting cell comprising the positive electrode film, the gel-stateelectrolyte separator film, and the lithium negative electrode wastested at the same conditions as the cell described in Example 2. Thetotal capacity delivered by this film was also in excess of 900 mAh pergram of the active-sulfur, that is, a utilization of 54% of theavailable sulfur, wherein 100% would be 1675 mAh/gm.

EXAMPLE 4 Solid-state cell: Total discharge capacity to 1500 mAh/gm ofsulfur evaluated at 90° C.

A positive electrode film similar to the one described in Example 1 wasmade for use at above ambient temperatures with a composition of 50%(weight percentage) elemental sulfur, 16% carbon black, polyethyleneoxide (900,000 molecular weight) and lithiumtrifluoromethane-sulfonimide (a 49:1 concentration).

The solid-state electrolyte separator used was cast from a slurry of900,000 MW PEO in acetonitrile without any additional electrolyte salts.The resulting electrolyte separator film weighed approximately 0.0048 gmper cm².

The cell was assembled as described in Example 1. Once assembled, thecell was compressed at 2 psi and heated at 90° C. for approximately 6hours. The cell was tested at 90° C. inside a convection oven located inthe glovebox. The cell was discharged to 1.8 V at rates of 500 to 100μA/cm².

The capacity relative to the sulfur versus the voltage during dischargeis shown in FIG. 5. The total capacity delivered by this film was alsoin excess of 1500 mAh per gram of the sulfur, that is, a utilization of90% of the available sulfur, wherein would be 1675 mAh/gm of the sulfur.

EXAMPLE 5 Solid-state cell: Cycling performance at a sulfur capacity of400 mAh/gm for each cycle evaluated at 90° C.

A positive electrode film similar to the one described in Example 4 wasmade with a composition of 50% (weight percentage) elemental sulfur, 24%carbon black, polyethylene oxide (900,000 molecular weight) and lithiumtrifluoro-methanesulfonimide (a 49:1 concentration). The electrolyteseparator is also the same as described in Example 4. The cell wastested at 90° C. and cycled to a constant capacity corresponding todelivering 400 mAh/gm of the sulfur in the positive electrode film. Therate used was 500 μA/cm² for discharge to 1000-500 μA/cm² for chargingat cutoff voltages of 1.8 and 2.6 volts, respectively.

FIG. 6 shows the end of the discharge voltage of the cell after eachrecharge cycle. As evident from the graph, the cell performance is veryconsistent.

EXAMPLE 6 Solid-state cell: Cycling performance for each cycle to acutoff voltage of 1.8 V evaluated at 90° C.

A positive electrode film identical to the one described in Example 4was made. The electrolyte separator is also the same as described hiExample 4. The cell was tested at 90° C. and cycled between voltagelimits between 1.8-2.6 volts. The rates used were 500-100 μA/cm² forcharging. FIG. 7 shows the delivered capacity after each recharge. Asevident from this graph most recharge cycles delivered above 1000 mAhper gram of the sulfur used in the cathode film.

EXAMPLE 7 Solid-state cell: Peak power performance evaluated at 90° C.

A positive electrode film similar to the one described in Example 4 wasmade with a composition of 50% (weight percentage) elemental sulfur, 16%carbon black, polyethylene oxide (900,000 molecular weight) and lithiumtrifluoromethanesulfonimide (a 49:1 concentration). The electrolyteseparator is also the same as described in Example 4. The cell wastested at 90° C. and pulse discharged for a 30 second duration or to acutoff voltage of 1.2 V. The discharge rates ranged from 0.1-3.5 mA/cm².The pulse power (W/kg) delivered by the cathode film versus the currentdensity is shown in FIG. 8. As seen from the plot, an extraordinarilyhigh pulse power of 3000 W/kg is capable of being attained.

The following table summarizes the performance of the representativebattery cells of Examples 1-7 under the specific testing conditionsdetailed in each example.

The following table summarizes the performance of the battery under thespecific testing conditions detailed in examples 1-7.

    __________________________________________________________________________               Result based on                                                               Cathode Film  Battery                                                                              Battery                                                                              Battery                                Temp, Type Performance*                                                                           # Cycles                                                                           Projections**                                                                        Projections**                                                                        Projections**                          __________________________________________________________________________    1 30° C., solid-state                                                              880 Wh/kg                                                                             N.A. 440 Wh/kg                                                                            550 Wh/l                                                                             440 Wh/kg                              2 30° C., solid-state                                                              300 Wh/kg                                                                             50+  150 Wh/kg                                                                            190 Wh/l                                                                             150 Wh/kg                              3 30° C., gel-state                                                                980 Wh/kg                                                                             N.A. 490 Wh/kg                                                                            610 Wh/l                                                                             490 Wh/kg                                component                                                                   4 90° C., solid-state                                                             1500 Wh/kg                                                                             N.A. 630 Wh/kg                                                                            790 Wh/l                                                                             630 Wh/kg                              5 90° C., solid-state                                                              400 Wh/kg                                                                             30+  200 Wh/kg                                                                            250 Wh/l                                                                             200 Wh/kg                              6 90° C., solid-state                                                             1000 Wh/kg                                                                             ˜10                                                                          500 Wh/kg                                                                            630 Wh/l                                                                             500 Wh/kg                              7 90° C., solid-state                                                             max: 3000 W/kg                                                                         N.A. 1500 Wh/kg                                                                           1880 Wh/l                                                                            1500 Wh/kg                             __________________________________________________________________________     *Mean voltage 2.0 V.                                                          **Assumed battery burden of 100%                                         

The demonstrated specific energies and specific powers listed above arebased on the entire composite positive electrode. The electrolyteseparators and lithium foils used for the laboratory tests were notoptimized for the final battery. The battery projections are based onusing 5 μm thick polymeric electrolyte separators, 30 μm thick lithiumfoil and 2.5-5.0 μm thick current collectors. Additionally, there is a10% weight increase allocated for the external casing assuming forbatteries larger than I Amphour.

Depending on the exact size and configuration of the cell laminate, thefinished battery performance is approximately 30-70% of the positiveelectrode film performance. For simplicity, 50% has been used for theconversion between positive electrode performance and batteryprojections (this is equivalent to 100% battery burden). The calculateddensity range of the battery ranged from 1.0-1.6 gm/cm³ depending on thespecific components and configurations. For simplicity, a density of 1.3gm/cm³ is used to calculate the projected energy density (Wh/l).

As evident from the table, the battery systems containing the positiveelectrode of this invention demonstrate exceptionally high specificenergies and exceed all now known solid-state intercalationcompound-based batteries. The cells of this invention also out performcells which operate at much higher temperatures such as theNa/beta-alumina/Na₂ S_(x) cell (350° C.), LiAl/LiCl, KCl/FeS₂ cell (450°C.).

It is seen that the invention provides high specific energy and powercells, the performance of which exceeds that of highly developed systemsnow known and in use. At the same time, the high energy and power areavailable at room temperature or ambient operation.

The foregoing describes the instant invention and its presentlypreferred embodiments. Numerous modifications and variations in thepractice of this invention are expected to occur to those skilled in theart. Such modifications and variations are encompassed within thefollowing claims.

All references cited herein are incorporated by reference.

I claim:
 1. A positive electrode comprising,a) active-sulfur; b) anelectronically conductive material mixed with the sulfur so thatelectrons can move between the sulfur and the electronically conductivematerial; and c) an ionically conductive material mixed with theactive-sulfur so that ions can move between the ionically conductivematerial and the sulfur, wherein at least about 10% of the active-sulfuris accessible to electrons and ionic charge carriers.
 2. The positiveelectrode of claim 1 wherein the positive electrode is electricallyconnected to a current collector.
 3. The positive electrode of claim 2wherein the electrode is operated between about -40 degrees Celsius andabout 180 degrees Celsius.
 4. The positive electrode of claim 3 whereinthe electrode is operated between about 30 degrees Celsius and about 90degrees Celsius.
 5. The positive electrode of claim 2 wherein theelectrode is deposited directly on the current collector as a thin filmelectrode having a thickness, t.
 6. The positive electrode of claim 5wherein components of the positive electrode are uniformly distributedsuch that each component's concentration does not differ by more than25% in a sample volume defined by half the thin film thickness cubed. 7.The positive electrode of claim 1 wherein the positive electrodecontains, between about 20% by weight to about 80% by weight,active-sulfur.
 8. The positive electrode of claim 7 wherein the positiveelectrode contains, between about 30% by weight to about 75% by weight,active-sulfur.
 9. The positive electrode of claim 8 wherein the positiveelectrode contains, between about 40% by weight to about 60% by weight,active-sulfur.
 10. The positive electrode of claim 9 wherein thepositive electrode contains, between about 45% by weight to about 55% byweight, active-sulfur.
 11. The positive electrode of claim 1 wherein theelectronically conductive material is selected from the group consistingof carbon black, compounds with conjugated carbon-carbon orcarbon-nitrogen double bonds, electronically conductive polymers,polyaniline compounds, polythiophene compounds, polyacteylene compounds,polypyrrole compounds, and combinations thereof.
 12. The positiveelectrode of claim 1 wherein the positive electrode contains, betweenabout 5% by weight to about 40% by weight, electronically conductivematerial.
 13. The positive electrode of claim 12 wherein the positiveelectrode contains, between about 8% by weight to about 30% by weight,electronically conductive material.
 14. The positive electrode of claim13 wherein the positive electrode contains, between about 8% by weightto about 24% by weight, electronically conductive material.
 15. Thepositive electrode of claim 1 wherein the ionically conductive materialof the positive electrode is provided in a solid-state form.
 16. Thepositive electrode of claim 15 wherein the the ionically conductivematerial is selected from the group consisting of polymericelectrolytes, ceramic electrolytes, glass electrolytes, beta aluminacompounds, and combinations thereof.
 17. The positive electrode of claim16 wherein the solid-state ionic conductor additionally comprisesbetween about 0.1% and about 20% aprotic organic liquid.
 18. Thepositive electrode of claim 15 wherein the solid-state ionic conductorcomprises electrolyte salts that form a complex with compounds selectedfrom the group consisting of polyether compounds, polyimine compounds,polythioether compounds, polyphosphazene compounds, polyalkylene oxidecompounds, polyethylene oxide compounds, amorphous polyethylene oxidecompounds, and combinations thereof.
 19. The positive electrode of claim15 wherein the aprotic organic liquid is selected from the groupconsisting of sulfolane compounds, dimethyl sulfone compounds,tetrahydrofuran compounds, propylene carbonate compounds, dialkylcarbonate compounds, ethylene carbonate compounds, dimethyl carbonatecompounds, butyrolactone compounds, N-methyulpyrrolidinone compounds,tetramethylurea compounds, dioxoyalane compounds, glyme compounds, ethercompounds, crown ether compounds, dimethoxyethane compounds, andcombinations thereof.
 20. The positive electrode of claim 15 wherein thepositive electrode includes a gelling agent is selected from the groupconsisting of polyvinylidine fluoride compounds,hexafluoropropylene-vinylidene fluoride copolymers, polyacrylonitrilecompounds, cross-linked polyehter compounds, polyalkyulene oxidecompounds, polyethylene oxide compounds, and combinations thereof. 21.The positive electrode of claim 1 wherein the positive electrodecontains an ionically conductive material in a gel-state.
 22. Thepositive electrode of claim 21 wherein the ionically conductive materialcomprises:a) between about 20% and about 80% of an aprotic organicliquid; b) gelling agents; and c) electrolyte salts.
 23. The positiveelectrode of claim 1 wherein the positive electrode further comprises atleast one of the following: binders, electrocatalysts, surfactants,dispersants, and protective layer forming additives.
 24. The positiveelectrode of claim 1 wherein the positive electrode is in a solid-stateform.
 25. The positive electrode of claim 1 wherein the positiveelectrode is in a gel-state.
 26. The positive electrode prepared by aprocess comprising:a) mixing active-sulfur, an electronically conductivematerial, and an ionically conducting material, in a solvent to form amixture; b) agitating the mixture for about two clays or until itappears uniform; c) casting a film of the mixture onto a surface; and d)allowing the solvent to evaporate, wherein at least about 10% of theactive-sulfur in the positive electrode is accessible to electrons andionic charge carriers.
 27. The electrode of claim 26 wherein the surfaceis an electrically conducting metal surface.
 28. The electrode of claim26 wherein the surface comprises an electrical connector to a currentcollector.
 29. The electrode of claim 26 wherein the surface is arelease film surface and the process comprises the additional step oftransfering the film to an electrical connector to a current collector.30. The electrode of claim 26 wherein the active-sulfur in the mixingstep is provided in a concentration of between about 40% and about 60%by weight before addition of solvent.
 31. The electrode of claim 26wherein the electronically conductive material is provided in aconcentration of between about 8% and about 30% by weight beforeaddition of solvent.
 32. The electrode of claim 26 wherein the ionicallyconducting material is selected from the group consisting of amorphouspolyethylene oxide polymers and polyethylene oxide polymers, saidpolymers complexed with electrolyte salts.
 33. The electrode of claim 32wherein the ionically conducting material contains lithiumtrifluoromethanesulfonimide and polymer in a concentration of betweenabout 1:8 and about 1:49 molecule of salt per monomer units.
 34. Theelectrode of claim 26 wherein the solvent comprises acetonitrile. 35.The electrode of claim 34 wherein the solvent to amorphous polyethyleneoxide ratio is between about 40:1 and about 200:1 by weight.
 36. Theelectrode of claim 26 additionally comprising the step of mixing aproticorganic liquid in amounts between about 0.1% and 20% by weight to thecomponents in step a) before adding solvent.
 37. The electrode of claim26 additionally comprising a step of removing solvent, water, or otherliquid traces by exposing the film to a vacuum with or without heat.